The invention relates to an ultrasound probe particularly for diagnostic purposes.
A typical structure of an ultrasound probe, particularly for an ultrasound probes used for ultrasound diagnostic imaging incorporates ultrasound transducers. These transducers are often piezoelectric elements, typically ceramic elements, which upon excitation with an electric potential are driven to oscillation of the ceramic crystal lattice, which generate mechanical waves in the frequency range of ultrasound acoustic waves. The frequency of the waves and the shape and spectral composition of the ultrasound waves generated depends on the frequency, shape and spectral composition of the electric excitation pulses.
Conversely, ultrasound transducers are capable of generating electric signals upon mechanical excitation of their crystal lattice by an impinging mechanical (e.g., acoustic) force or waves. The frequency range, shape and spectral composition of the generated electric signal depends on frequency range, shape and spectral composition of the impinging acoustic waves, for example.
The same transducer array may be used alternatively as a receiving and as an emitting device for converting electric excitation pulses into acoustic pulses and acoustic excitation pulses into electric pulses.
In a typical ultrasound probe, a transmission and receipt switch is provided which after each excitation by electric signals the emission of acoustic waves turns the conductors of the electric signals associated with the transducers to a receipt section of an ultrasound system by which the electric signals generated by the impinging reflected acoustic waves are elaborated or analyzed in order to extract information such as, for example, image data. Due to the fact that the probe is connected by means of a cable having a certain length and having a high capacity with respect to the power of the electric signals generated by the transducers upon acoustic excitation. It would be desirable to have each transducer further connected to a preamplifier, or just a signal follower, which enhances the signal power in order to allow its conduction through the cable, thus improving the sensitivity and/or the bandwidth.
The problem of the power of the electric signal does not arise for the excitation signals sent to the transducers, since a dedicated section generates these signals and the power of the signals can be adjusted easily at a level ensuring the correct transmission to the transducers.
Nevertheless in using the same transducers for emission of ultrasound waves and for receipt of ultrasound waves causes some problems for the preamplifiers that have to be rather complex, since, due to the fact that the same conductor line is used for transmitting the excitation signals to the transducers and for collecting the receipt signals generated by impinging reflected ultrasound waves from the transducers, the preamplifiers need a decoupling section to avoid shortcuts during transmission of the excitation signals to the transducers.
These decoupling circuits need several components which increase the physical dimensions of the preamplifier in a dramatic way. The dimensional part of the preamplifier due to the decoupling circuits can be even greater that the one needed for the preamplifier itself. Furthermore the decoupling circuits give rise to major costs due to a more complicated structure of the preamplifier and to higher costs for miniaturization by means of the actual techniques of integration.
On the other hand the use of the same array of transducers for generating and emitting the ultrasound transmission waves and for receiving the reflected ultrasound waves reduces the dimensions and the weight of the probe itself which, particularly for diagnostic applications, is very important due to the fact that the probe is manipulated mostly by hand.
Providing two different array of transducers, one of which is only dedicated to generating the ultrasound transmission waves and the second of which is only dedicated to receiving the reflected or impinging ultrasound waves, would overcome the above mentioned problems. On the other hand, considering matching of the acoustic impedance, acoustic separation and electric separation of the two transducer arrays, this solution would lead to a considerable increase of the dimensions and of the weight of the probe.
Another possible way of solving the above problem would consist in using only part of the transducer of the array for generating and transmitting the ultrasound waves and part of the transducers of the array only for receiving the impinging or reflected ultrasound waves. This solution also solves the above mentioned problems and no increase in the overall dimensions of the probe would be caused by this solution. On the other hand, using only part of the transducers for transmitting and for receiving the ultrasound waves would cause a reduction of the quality of the data extracted from the reflected ultrasound beams, such as power of the reflected ultrasound waves and image definition.
A third aspect has further to be considered which has a particular relevance in ultrasound diagnostic imaging and which is related to the matching layers. These layers must match the acoustic impedance of the transducers with the one of the body under examination but the matching must be achieved without reducing the bandwidth of the probe either for the case of the transmission of the ultrasound waves and in the case of the receipt of the reflected ultrasound waves. This aspect is relevant in the case of two different arrays of transducers being used independently for transmission and for receipt of the ultrasound waves. Thus using two separate arrays of transducers laid one over the other would cause problems for matching the acoustic impedance and furthermore for ensuring at the same time the expected or needed pass bandwidth.